In electrophotography, also known as Xerography, electrophotographic imaging or electrostatographic imaging, the surface of an electrophotographic plate, drum, belt or the like (imaging member or photoreceptor) containing a photoconductive insulating layer on a conductive layer is first uniformly electrostatically charged. The imaging member is then exposed to a pattern of activating electromagnetic radiation, such as light or a laser emission. The radiation selectively dissipates the charge on the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image on the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic marking particles on the surface of the photoconductive insulating layer. The resulting visible image may then be transferred from the imaging member directly or indirectly (such as by a transfer or other member) to a print substrate, such as transparency or paper. The photoconductive layer is an insulator in the dark so that electric charges are retained on its surface. Upon exposure to light, the charge is dissipated. The imaging process may be repeated many times with reusable imaging members.
As more advanced, higher speed electrophotographic copiers, duplicators and printers have been developed, and as the use of such devices increases in both the home and business environments, degradation of image quality has been encountered during extended cycling. Although excellent toner images may be obtained with multilayered belt or drum photoreceptors, it has been found that as more advanced, higher speed electrophotographic copiers, duplicators and printers are developed, there is a greater demand on copy quality. A delicate balance in charge, discharge, and bias potentials, and characteristics of the toner and/or developer, must be maintained.
One type of printing defect is referred to as “ghosting,” which includes “transfer ghosting,” “image ghosting,” as well as other types of ghosting. While not wishing to be bound to any theory, one cause of this defect is believed to be photoreceptor damage caused by positive-charge injection. Positive charge injection is the injection of a positive charge from the surface of the photoreceptor to the bulk of the photoreceptor, which is believed to cause a shadow or ghost of an image to be transferred along with subsequent images.
Thus, there is a need for electrophotographic photoreceptors and electrophotographic techniques for preventing positive charge injection and related damage to photoreceptors, and to reduce or eliminate ghosting.